The study tests whether an inhibitor of asparaginase (ASNase), 5-diazo-4- oxo-L-norvaline, added to blood drawn from leukemic patients treated with ASNase, results in a better assessment of blood asparagine (ASN) levels. thus, better therapeutic management of the disease would result. While no patients were admitted to the CRC, the Core laboratory developed an HPLC method or quantitative determinations of ASN in plasma (71 determinations) and has completed a study of 119 patient samples.